Continuum bands

Figure 6.9. Formation of an electron band by addition of atoms and their orbitals. Note that the splitting between the bonding and antibonding levels increases by increasing the overlap. Eventually, when a high number of orbitals are added, a continuum band is formed as illustrated by the shaded region on the lower panel.

Because the continuum bands are equally spaced in /X, these double indices are relatively insensitive to Teff and reddening, for which small corrections are applied. 

Figure 3.9. The Fourier transform of spectra of Fig. 3.8 Projection PK(a>) of the pure excitonic state on the eigenstates of the coupled system of an exciton K and the effective photon continuum in a 2D lattice, for various values of the wave vector K (KXd). The vertical peak represents a discrete state, whose weight is represented by a rectangle (a-d). For an exciton with K < K0, the continuum band (matter-contaminated photons) dominates the spectrum, with a quasi-lorentzian resonance (a,/). For K > K0, the discrete state dominates (d,e). In the intermediate region (b, c) the spectrum reflects the complicated behavior of its Fourier transform cf. Fig. 3.8. 

The separation of the continuum from emission features is a difficult problem. There are numerous unidentified emissions [57] that can form a pseudocontinuum of gas-rich comets. It is not clear whether the continuum is reached in the continuum bands therefore, we can conclude that at least a part of the gas-rich comets have a low polarization at large phase angles and blue color mainly due to a low spectral and spatial resolution of observations. Thus, the existence of two taxonomical classes of comets with different physical properties of their dust particles still remains an open question. 

The effects of the fourth case will be seen if the absorption band of a molecule existing in the flame is located at the same wavelength as the resonance line of the analyte. Molecular absorption spectra obtained from several alkali and alkaline earth halides are shown in Figure 44. The effects of continuum band absorption and scatter are discussed in detail in the sections on Background Correction (Section 5). 

One of the most notable examples of the application of EA spectroscopy to organic semiconductors is polydiacetylene, in which EA spectroscopy was able to separate absorption bands of quasi-ID excitons from that of the continuum band [78]. The confined excitons were shown to exhibit a quadratic Stark effect, where the EA signal scales with and the EA spectrum is proportional to the derivative of the absorption with respect to the photon energy. In contrast, the EA of the continuum band scales with and showed Frank-Keldish (FK) type oscillation in energy. The separation of the EA contribution of excitons and continuum band was then used to obtain the exciton binding energy in polydiacetylene, which was found to be -0.5 eV [78]. 

Figure 15.8 Oscillatory continuum emission X > 285 )nm from I2(f0+). Below A = 285 nm the emission is to bound states and shows normal ro-vibrational structure. The difference between the two types of emission is difficult toseeatA = 285 nm, due to the limited resolution. However, the difference is clearly ro-seen at the two ends of the spectrum sharp ro-vibrational structure is seen atX— 260 nmand broad oscillatory continuum bands ztX = 340 nm...

As seen in Fig. 4.39(a), absorption spectrum of HOCl consists of a fairly strong continuum band with a peak at around 240 nm and a second continuum which appears as a shoulder at around 300 nm. These transitions have been assigned to 2 A l A, l A" l A, respectively. Table 4.32 gives absorption cross sections of HOCl extracted from NASA/JPL Evaluation No. 17 (Sander et al. 2011) based on Burkholder (1993) and Barnes et al. (1998). 

The absorption spectrum of HOI has been reported by Bauer et al. (1998) and Rowley et al. (1999). Figure 4.39(c) shows the absorption spectrum by Bauer et al. (1998), and Table 4.32 gives the absorption cross sections recommended by NASA/JPL Evaluation No. 17 (Sander et al. 2011) taking the average of above two studies. As can be seen in Fig. 4.39(c), the absorption spectmm of HOI consists of continuum bands with two peaks at 340 and 408 mn. 

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